About Irinotecan A topoisomerase 1 inhibitor,Natural Source (Plant) Derivative ,semisynthetic camptothecin analogue , Antineoplastic. Mechanism of Action of Irinotecan Binding of Irinotecan and its active metabolite bind to the topoisomerase 1 (which catalyze recombination, repair of DNA and also reversible single strand breaks in DNA during DNA replication) and form a topoisomerase1-DNA complex and this prevents relegation of these single strand breaks, finally cell death. Interactions for Irinotecan Other antineoplastic agents: Side effects like diarrhoea and myelosuppression may be exacerbated. Dexamethasone: Lymphocytopenia has been observed when coadministered. Diuretics: Because of possibility of causing dehydration with diarrhoea, caution should be observed in the use of irinotecan with diuretics.